Hi,
Thanks for your replies.
I have performed some profiling with Clang passing a `path` to the lambda
instead of `const char*` and the performance gain are effectively reduced
as stated by Nicol Bolas.

For this reason, i have changed the proposal to add both solutions: a new
recursive_directory_iterator constructor with predicate concept on `path` (
for generality) and a new recursive_directory_iterator constructor with
predicate concept on `const char *` (mostly for performance gain, as
profiling shows, we can divide execution time by two, and even more..)

I have added a subsection "Passing a path or passing const char* to the
predicate concept" at "Analysis and Discussions" section, explaining this,
and have taken into account your other comments.

Please, find attached the new draft proposal.

Thanks,
Noël.